Method of stabilizing hydrocarbons



Patented Aug. 9, i949 UNITED STATES PATENT OFFICE 2,473,710

METHOD OF S'TABILIZING HYDROCARBONS Richard F. Robey, Granford, N. J., assignor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application December 21, 1945, Serial No. 636,498

7 Claims. (01. zoo-seat) This invention relates to stabilizing hydrocarbo'ns, and particularly of minimizing oxidation and polymerization through the employment of inhibitors.

The instability of hydrocarbon mixtures produced in petroleum refineries, especially of cracked gasolin'es and certain lubricating oils, has been extensively studied. The changes which have been found to occur in these hydrocarbon mixtures in contact with air or oxygen are considered due primarily to auto-oxidation reactions wherein there are formed oxidized, condensed and polymerized compounds which either remain in the solution or in time separate as gummy deposits which adversely affect the quality of the material or interfere with processing in the refinery. The use of various type compounds in relatively small proportions as inhibitors is a common means of combating such instability. In some cases, the inhibitor employed consists of a single compound, while in other cases it is a mixture of compounds, such as in co-pending application U. Serial No. 537,540, filed April 26, 1944, now U. '8. Patent No. 2,445,367. The present invention is concerned with a mixture of compounds-as an inhibitor composition, the particular advantage in the admixture being the uniqueness of its liquid condition.

In the manufacture of synthetic rubber and synthetic resins, the lower molecular weight diolefins are used as basic materials. Thus, butadiene, isoprene, cyclopentadiene, and the miserylenes are commonly extracted in high degrees of purity as raw materials for the .preparation of important synthetics. Unsaturated compounds such as styrene are also employed. In handling and processing unsaturated hydrocarbons, control of stability is important, especially from the point of view of plant safety and minimizing the loss of production time due to stoppage of equipment with solid polymers. In shipment and storage before use, good stability is necessary for maintenance of product quality and suitability for various purposes. The formation of the high molecular weight polymers from unsaturated monomers has been shown to be catalyzed by the presence of peroxides which are easily formed upon exposure of the material itself to an atmosphere containing oxygen or to peroxide catalysts. (Robey et 211., Ind. Eng. Chem. 36, 3 (1944).)

In the use of inhibitors, particular difiiculty is often presented in the means by which the compounds may be added. In the case of solid materials, concentrated solutions are commonly prepreparation and storage of concentrates are be set with many difilculties. In the present in vention, uniqueness of the inhibitor composition is that two different inhibitor type compositions are employed which exert a liquefying efiect one upon the other. Particular examples of the applicants compositions have liquid consistencies at temperatures well below those individual compounds by reason of their association together in proportions approximating that of an eutectic for the combination of the substances. In other words, the inhibitor compositions of the present invention are highly concentratedinhibitor mixtures, the liquid condition of which is obtained as a result of a mutual blending effect approaching eutectic conditions as the final low temperature blend.

The liquid inhibitor compositions of the invention consist of mixtures of substituted polyhydroxy-benzenes, preferably a 'catechol in which the substituent is preferably, but not necessarily, an alkyl chain, and a naphthol, that is, either alpha or beta naphthol of substituted or unsubstituted character. The alkyl substituted catechols and the naphthols are normally solid ma-- terials under ordinary atmospheric conditions. When blended together, however, with the catechol in the predominant proportion, the blends can be made to assume a composition melting below room temperature. The inhibitor conipositions of this invention are the liquid blends of such substituted catechols and naphthols.

flhus, it has been found that solid tertiary butyl catechol is particularly efiective as an inhibitor in hydrocarbon polymerization systems at temperatures ranging from about 20 C. to about 60. or C. Alpha naphthol, on the other hand, is relatively more efifective as an inhibitor for hydrocarbon polymerization reactions at temperatures of about 110 C., but not so efiective at lower temperatures. When either of the substances is added alone to plant equipment, difficulties occur in the process of solution of the inhibitor, also difficulties in control of their rate of addition. Moreover, the range of maximum effectiveness of the single inhibitor is limited. However, when a mixture comprising about tertiary butyl catechol and 10% alpha naphthol are compounded together, a liquid mass is ob tained at normal conditions (25 C.) This liquid blend of the two inhibitors is effective as an inhlbitory material for hydrocarbon polymeriza- Fraction of ctive i a Inhibitor Oxygen Destroyed Per Hour 80"-.- None 0.00 80 Tertiary Butyl Catechol; 0. 18 80...... Alpha Naphthol "I; 0.06 110 None 0.00 110..-. Tertiary Butyl Catechol 0.21 110.... Alpha Naphthol 1.0

The disappearance of active oxygen was followed by the well-known ferrous thiocyanate colorimetric method. These data show the relative'superiority of tertiary butyl catechol at temperatures of about 80 C., while alpha naphthol is more effective at temperatures of about 110 C. When a mixture of 90% by weight of tertiary butyl catechol (solid at 52 C.) and alpha naphthol (solid at 96 C.) was prepared, a liquid freezing at 25C. was obtained. The liquid so obtained is mobile, easily handled and pumped The following data were ob-.

through pipes. tained in connection with the polymerization of essentially pure isoprene at 100 C. in the presence of 100 parts per million of peroxides calculated as active oxygen:

Rate of Polymerization to High Polymer, Weight Percent Per Hour Inhibitor None 0.22% Mixture Tertiary Butyl Catechol and Alpha Naphthol This mixture is, moreover, easily removable from hydrocarbon solution by Washing the solution with dilute caustic soda solution or by simple amount of a liquid mixture consisting of a naphthol and an alkyl catechol, said mixture having a melting point below that of either said components and being a liquid at room temperature.

2. A composition of matter stabilized against oxidation and polymerization which consists of a cliolefin hydrocarbon and a stabilizing amount of a liquid mixture consisting of a naphthol and an alkyl catechol, said mixture having a melting point below that of either said components and being a liquid, at room temperature.

3. A composition of matter according to claim 2 in which the liquid mixture consists of about 90% alkyl catechol and 10% naphthol and being a liquid at room temperature.

4. A composition of matter according to claim 3 in which the liquid mixture consists of about 90% tertiary butyl catechol and 10% alpha naphthol and being a liquid at room temperature.

distillation of the hydrocarbons boiling below What is claimed is: 1. A composition of matter stabilized against oxidation and polymerization which consistsof an unsaturated hydrocarbon and a stabilizing 5. A composition of matter stabilized against oxidation and polymerization which consists of butadiene and a stabilizing amount of a liquid mixture consisting of a naphthol and an alkyl' catechol, said mixture having a melting point below that of either said components and being a liquid at room temperature.

6. A composition of matter stabilized against oxidation and polymerization which consists of isoprene and a stabilizing amount of a' liquid mixture consisting of a naphthol and an alkyl catechol, said mixture having a melting pointbelow that of either said components and being a liquid at room temperature.

7. A composition of matter stabilized against oxidation and polymerization which consists of cyclopentadiene and a stabilizing, amount of a liquid mixture consisting of a naphthol and an alkyl catechol, said mixture having a melting point below that of either said components and being a liquid at room temperature.

' RICHARD F. ROBEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES IE A'IIEINTS 

